From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 74C67C4727E for ; Thu, 1 Oct 2020 16:55:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12F532075F for ; Thu, 1 Oct 2020 16:55:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="rebj3f3A" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732213AbgJAQzI (ORCPT ); Thu, 1 Oct 2020 12:55:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732016AbgJAQzI (ORCPT ); Thu, 1 Oct 2020 12:55:08 -0400 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 27440C0613D0 for ; Thu, 1 Oct 2020 09:55:08 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id j136so2589396wmj.2 for ; Thu, 01 Oct 2020 09:55:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=6thW6uIzKo0AKUx3z1dt90fnAdUCuGiPlcRQ/kj9HnY=; b=rebj3f3AW67QJeOWEtUX9RtfI0VlOpeM7wzL14FFUmiUbt2QR4NSbV+Q3ZiYp7Xr3Q KoFT2KMbqOLiKx4Uq6qJT2tegAsfod11DOnwtiAGfslzlckXhHz0r9Z+9Khm+jqgAjMp UMCUOQTQ9JYFawI2uGsNpBzA3OICD8y4eNhQnsu0wg6KWonR0xkrjsWE9LYzfu3IxY5q aUFMP5UfoFfRAxl3xrvv0L/CaEOwRkQTBCN8yaBtfAXaBSXtl/qVFVvg3U8YbWHwTOo7 Km81tJyIIW7KKtT0aqHFoN+wUhLy6A0fvyIS+fqVDZngngHRfeXAqEEAzXTI9Lc8yPe+ gocg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=6thW6uIzKo0AKUx3z1dt90fnAdUCuGiPlcRQ/kj9HnY=; b=H0JZSZb+k2ZHCdxiIwQe8nIBdkQ40xn9pvFKAlXgQYjkdP4XWUonVtkISSfvXdK+gz 9CWRoYdKJiz6Q4AnEW0r9AoFlUUTadCVjSfh4WauA/C+6j1de1pie8aUxls/1p7BmdmO c5fFjpKdBm4REIQtQ4sJ+Q1mQd19DiX1q66D7aQMEA/kIrJfaFmGURm6B0KXH4qw8A6M /nbU66FvMrnjM13CpafdTmc6RnMuEh5f+vr1R8B0oYWdj7fxFG29SdGFN2D8n+wxxUSe J4KVPG/AQKQ2T3IN9oU/AlSM+KGoOuVCqtExdeHieyoX6fr1Cc8tocXp4xf/6yg8p/Ni FAfQ== X-Gm-Message-State: AOAM531kPbpsskxHHXC6LTk5QiSgnPC8Xm3JdesrFtST+OPFYEJ75uBh C+MBbKNUC86NC9QoALUGqkw= X-Google-Smtp-Source: ABdhPJynBwL8B/dPnbv/POOgme/EYgQ8xb2q9YNIKii1u4FdsmU899H5MSVGe6Nc3+BzGOiOrDfrNg== X-Received: by 2002:a05:600c:215:: with SMTP id 21mr921762wmi.105.1601571306836; Thu, 01 Oct 2020 09:55:06 -0700 (PDT) Received: from [192.168.1.143] ([170.253.60.68]) by smtp.gmail.com with ESMTPSA id n2sm858530wma.29.2020.10.01.09.55.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Oct 2020 09:55:06 -0700 (PDT) Subject: Re: [PATCH v2 1/2] system_data_types.7: Add 'void *' To: "Michael Kerrisk (man-pages)" Cc: linux-man@vger.kernel.org, gcc@gcc.gnu.org, libc-alpha@sourceware.org References: <41affebd-3354-9420-0048-bffd14535e95@gmail.com> <20201001154946.104626-2-colomar.6.4.3@gmail.com> From: Alejandro Colomar Message-ID: <41ab7ed9-3ce0-f8ad-38f4-c4bbeca138f8@gmail.com> Date: Thu, 1 Oct 2020 18:55:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org On 2020-10-01 18:38, Michael Kerrisk (man-pages) wrote: > Hi Alex, > >> +According to the C language standard, >> +a pointer to any object type may be converted to a pointer to >> +.I void >> +and back. >> +POSIX further requires that any pointer, >> +including pointers to functions, >> +may be converted to a pointer to >> +.I void >> +and back. > I know you are correct about POSIX, but which part of the > standard did you find this information in? The only > reference that I find in POSIX is the dlsym() spec. Is it > covered also somewhere else in the standrd? > > Thanks, > > Michael > Hi Michael, I've bean searching, and dlsym is the only one: ________ user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "pointer to a function" functions/regfree.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/dlsym.html:138:

Note that conversion from a void * pointer to a function pointer as in:

functions/regcomp.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/regexec.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/V2_chap02.html:3039:

There are three types of action that can be associated with a signal: SIG_DFL, SIG_IGN, or a pointer to a function. Initially, functions/regerror.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "function pointer" basedefs/glob.h.html:165:"../functions/glob.html">glob() prototype definition by removing the restrict qualifier from the function pointer xrat/V4_xsh_chap02.html:114:when the application requires it; for example, if its address is to be stored in a function pointer variable.

functions/dlsym.html:138:

Note that conversion from a void * pointer to a function pointer as in:

user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "pointer to function" functions/dlsym.html:73:converted from type pointer to function to type pointer to void; otherwise, dlsym() shall return the address of the user@debian:~/Desktop/src/Standards/susv4-2018$ From those, the only one that documents this is functions/dlsym. The rest is noise. The most explicit paragraph in dlsym is the following: [[ Note that conversion from a void * pointer to a function pointer as in: fptr = (int (*)(int))dlsym(handle, "my_function"); is not defined by the ISO C standard. This standard requires this conversion to work correctly on conforming implementations. ]]